1. Field of the Invention
The invention relates to an apparatus for testing for the presence of trace amounts of a contraband material on the surface of an object.
2. Description of the Related Art
Terrorism risks continue to increase at transportation facilities, government buildings, banks, restaurants, hotels and other locations where there is a significant flow of pedestrian or vehicular traffic.
Airlines now routinely screen passengers and employees for explosives. Screening typically is carried out in several stages. For example, all passages are required to pass through a metal detector and all baggage is required to pass through an X-ray apparatus. However, a plastic explosive device could be concealed on a person or in a piece of luggage in a manner that might not be detected by a conventional metal detector or an X-ray apparatus. Even a small amount of a plastic explosive can cause sufficient damage to bring down an aircraft.
Most airports now include apparatus for detecting trace amounts of explosives. These devices operate on the principle that small amounts of the explosive materials will be transferred to the body, clothing and luggage of people who had handled the explosive. Some detectors employ small flexible fabric-like traps that can be wiped across a package or piece of luggage. The trap removes residue from the surface of the package or luggage. The trap then is placed in an apparatus, such as an ion trap mobility spectrometer, that tests the residue on the trap for trace amounts of explosive materials. A device of this type is disclosed in U.S. Pat. No. 5,491,337 and is marketed by the GE Ion Track. These devices typically are employed in proximity to the metal detectors, and security personnel will perform screening on some of the passengers based on a random sampling or based on a determination that the passenger has met certain criteria for enhanced screening.
The ion trap mobility spectrometer disclosed in U.S. Pat. No. 5,491,337 also can operate in a mode for detecting trace amounts of narcotics. Narcotics are illegal and insidious. Furthermore, it is known that many terrorists organizations fund their terrorism through the lucrative sale of narcotics.
The above-described ion trap mobility spectrometer and similar devices have been accepted at airports in view of the notorious efforts of terrorist groups to attack commercial airliners. The above-described detectors have not been accepted widely at other potential targets of terrorism, including train stations, bus terminals, government buildings and the like. The screening of personnel entering train stations, bus depots, government buildings and such by the above-described detection devices would significantly slow the flow of people into and through such buildings and would impose a significant cost penalty on the operators of such facilities.
Only a fraction of airline passengers have their baggage checked for trace amounts of explosives or narcotics using the available ion trap mobility spectrometers and similar devices. Efforts to use such devices to check all bags for trace amounts of explosives or narcotics would impose greater time and cost penalties on the airline industry. Additionally, explosive detectors typically are used only on luggage and other parcels. An apparatus of this type would not identify plastic explosives worn by a passenger who had no carry-on luggage.
U.S. Pat. No. 6,073,499 discloses a walk-through detector. The detector shown in U.S. Pat. No. 6,073,499 operates under the principle that a boundary layer of air adjacent to a person is heated by the person. This heated air adjacent a person is less dense than air further from the person. Less dense air rises. Accordingly, a thermal plume of air flows up adjacent to a person. Minute particles, including particles of explosives or narcotics, will be entrained in this thermal plume of air and will flow upwardly from a person. The walk-through detector disclosed in U.S. Pat. No. 6,073,499 employs an ion mobility spectrometer or ion trap mobility spectrometer to detect microscopic particles of interest that are likely to be entrained in the thermal plume of air flowing upwardly adjacent to a person who walks through and pauses briefly in the detector. The walk-through detector disclosed in U.S. Pat. No. 6,073,499 is very effective for detecting whether a person is carrying explosives or narcotics and whether the person has recently handled explosives or narcotics.
A person who had handled explosives or narcotics is likely to have microscopic residue of the explosive or narcotic materials on his or her fingers, and trace amounts of the explosive or narcotic will be transferred to objects that are handled by the person. For example, it has been assumed that residue of such contraband will be transferred from the fingers to an airline ticket, a boarding pass or an identification card. Hence, the contraband conceivably could be detected on the ticket, pass or card. Efforts have been made to develop a detector that identifies particles of interest on such a card-like object. One such effort used a fabric-like trap, similar to those used to wipe down luggage. The trap was mounted on a heated metal drum that would be rotated against a surface of the card-like object being tested. These efforts have not proved to be commercially successful because of the potential for damage to the ticket or boarding pass due to heat generated by the detector. The trap could be cooled between tests, but such cooling would add significantly to the cycle time. Additionally the fabric traps were found to soil quickly and hence required frequent changing.
In view of the above, it is an object of the invention to provide an apparatus for testing the surfaces of substantially planar sheet-like materials for the presence of explosives, drugs or other substances of interest.